I've got a Hagon on my '92 R100GS. It seems to work perfectly well as far as I can tell, absolutely no complaints performance wise and not a hint of oil loss or anything, but the finish on it rotted off in three years flat and I've had to strip it, powder coat the spring and re-spray the body.
Admittedly the bike doesn't get pampered - it's in regular use all year and might get cleaned once or twice a year if its lucky, so the shock is covered in mud / salt etc for much of the time. I suppose it depends on what how you use the bike, but I'd like to hope that a shock for a rugged bike would cope with winter use without requiring a clean every time out. Or maybe I was just unlucky and got one with a duff finish?
Any comments on how the finish on Ohlins / WP / Wilbers etc survive the winter salt?
Cheers.